Acoustic method for treatment of stuck pipe in a well



W. B. BROOKS Sept. 3, 1968 ACOUSTIC METHOD FOR TREATMENT OF STUCK PIPE IN A WELL 2 Sheets-Sheet 1 Filed Dec.

FIG.

WARREN B. BROOKS INVENTOR IMI/ ATTORNEY p 1968* w. B. BROOKS 3,399,724

ACOUSTIC METHOD FOR TREATMENT OF STUCK PIPE IN A WELL Filed Dec. 5. 1966 2 Sheets-Sheet 2 FIG. 2

WARREN B. BROOKS INVENTOR B mtl/v-m ATTORNEY United States Patent 3,399,724 ACOUSTIC METHOD FOR TREATMENT OF STUCK PIPE IN A WELL Warren B. Brooks, Dallas, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed Dec. 5, 1966, Ser. No. 599,301 16 Claims. (Cl. 166-4) This invention relates to the acoustic treatment of pipe strings stuck within wells and, more particularly, to methods of locating the depth at which a pipe string is stuck and of loosening the string by torsional vibration.

Oftentimes in drilling or operating wells such as oil or gas wells, a pipe string may become stuck at some subterranean location within the well. For example, in the rotary drilling of a well the drill string may become stuck or frozen at a location well below the surface of the earth. This may result from one or more of a number of causes. For example, the drill pipe may become stuck as the result of drawing the pipe upwardly through a keyseat in the well which may be formed by abrasion of the drill pipe against the side of a crooked portion of the well. As the drill string is withdrawn from the well, a drill collar, i.e., a relatively heavy length of pipe near the bottom of the drill string, may become lodged in the keyseat. The drill string also may become stuck as the result of cuttings which settle within the hole and accumulate about the lower end of the drill string. Also, the drill string may become stuck as a result of the walls of the well caving in at some location.

Regardless of the cause, a stuck drill pipe must be freed before normal drilling operations can be resumed. Numerous techniques have been developed for loosening stuck drill strings as well as other pipe strings, such as casing, tubing, etc. One conventional practice involves twisting off the pipe string at ajoint immediately above the stuck point and thereafter enlarging the hole in the vicinity of the stuck point. The pipe string thus freed then can be withdrawn from the well by conventional fishing practices. Of more recent advent are the socalled sonic jarring techniques in which mechanical vibrations in either a longitudinal or a torsional mode are imparted to the pipe string and transmitted through the string to the stuck location. By these techniques an attempt is made to vibrate the pipe string at the stuck locaion, thus freeing it from the surrounding earth material or other binding medium.

The present invention involves a new and improved acoustic method of loosening a stuck pipe string by imparting to the pipe string torsional vibrations which are controlled with regard to wave length and frequency so as to cause significant displacement of the pipe string within the stuck location. In carrying out this aspect of the invention, the pipe string is clamped against torsional vibration thereof at a 'firstp'oint remote from the location at which the pipe is stuck within the well. Torsional vibrations are applied to the pipe string at a frequency such that quarter-wave or multiple quarter-wave oscillation occurs between the first point and a second point at which the torsional vibrations are applied to the pipe string. The first point thus becomes a displacement node in the vibrating system and the second point an antinode. The first and second points are spaced with regard to a third point within the stuck location of the pipe such that halfwave or multiple half-wave oscillation occurs between the second and third points within a tolerance range of plus or minus A; wave length. Thus, the relationship between wave length and these three points is such that significant displacement is forced to occur at the third point. In a preferred embodiment of the invention, these relationships -are such that half-wave or multiple-half wave oscillation occurs between the second and third points such that the third point becomes a displacement antinode in the acoustic system.

The above-described embodiment of the invention requires a relatively precise determination of the subterranean location within the well at which the pipe is stuck. In accordance with another aspect of the invention, there is provided a simple and accurate method for determining this location. In carrying out this aspect of the invention, the upper portion of the pipe string adjacent the surface of the well is placed in a condition of low acoustic impedance permitting rotational movement. While the upper portion of the pipe string is maintained in this condition, a torsional force is applied to the pipe string and then released in order to cause free torsional oscillation of -the pipe string. The frequency of this torsional oscillation is measured in order to determine the depth at which the pipe string is stuck. Thereafter, the aforedescribed method of loosening the pipe string may be applied.

For a better understanding of the present invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an illustration, partly in section, showing an environment in which one aspect of the invention may be carried out; and

FIGURE 2 is an illustration, partly in section, showing an environment in which another aspect of the invention may be carried out.

The following detailed description is given with regard to the rotary drilling of a well, in connection with which the invention will find its greatest usefulness. However, it is to be understood that the invention may be carried out with regard to well pipe which becomes stuck during other operations. For example, the invention is applicable to a casing or tubing string which is stuck at a subterranean location within a well.

With reference to FIGURE 1, there is shown a rotary drilling rig for drilling a well 2 through the earths crust. Drilling operations are carried out utilizing a rotary drill bit (not shown) which is attached to the lower end of a drill string 4. The drill string comprises a kelly 6 and joints of drill pipe 7. The kelly 6 is polygonal, e.g., hexagonal or square, in cross-section and extends through a rotary table 9. The kelly 6 is received within the rotary table 9 in a slidable torque-applying relationship by means of a kelly bushing (not shown). The rotary table 9 is powered by a prime mover 10 through a suitable drive mechanism such as a chain drive 12 in a manner well known to those skilled in the art.

The drill string is suspended from the derrick structure 14 of the drilling rig by means of a hook 16 which is attached to a traveling block .17. The traveling block in turn is suspended by means of a cable 19 from a crown block (not shown) in the upper portion of the derrick. The kelly 6 is connected to the hook 16 through a rotary swivel 21 which permits rotation of the drill string relative to the hook and traveling block. Drilling fluid is circulated through a flexible conduit 22 into the swivel 21 and thence through the interior passage of the drill string to the bit at the bottom thereof. The drilling rig is supported on a suitable substructure which may take the form of a derrick floor 24 and a plurality of piers 26 or other foun dation elements. Also, as shown in FIGURE 1, the well normally is provided with a conductor system which may include a conductor pipe 28 set into the well as well as other equipment (not shown) such as a blowout preventer.

For the purpose of describing the present invention it will be assumed that the drill string 4 has become stuck at a subterranean location within the well generally indicated by reference numeral 30. Such stuck condition may have occurred by reason of sloughing or caving in of the borehole with the result that earth material 32 securely binds the drill string 4 such that rotational movement thereof cannot occur at the stuck location. It will be understood, however, that such stuck condition may have occurred from other causes such as those mentioned above.

In order to loosen the drill string 4 in accordance with the present invention, it first becomes necessary to determine the depth at which the drill string is stuck. This may be accomplished in accordance with one aspectof the present invention by causing free torsional oscillation of the drill string under conditions such that a node occurs at the stuck location of the drill string and an antinode at the upper end thereof. As a first step in this embodiment of the invention, the upper portion of the drill string adjacent the surface of the well is placed in a condition permitting rotational movement thereof. This may be accomplished by disengaging the rotary table 9 from the prime mover so that it turns freely. Since the connection of the kelly to the hook 16 will dampen torsional oscillation somewhat, the kelly may be suspended in the drill table through the use of slips in a manner well known in the art and the kelly then disconnected from the traveling block. In most cases, however, such dampening w ll be of little significance and the drill string 4 may remam suspended from the traveling block as shown.

The drill string is provided with a system for measuring the frequency of torsional oscillations thereof. This takes the form of suitable frequency-sensing means 34 which measures the frequency of torsional oscillations and generates a signal in response thereto which is communicated through a suitable communications channel, indicated by broken line 36, to a recorder 38. By way of example, the frequency-measuring system may take the form of strain gauges which are secured to the drill string and connected in a conventional Wheatstone-bridge type measuring circuit which includes a suitable source of DC power, such as a battery, and the recorder 38. Since such means for measuring and recording the frequency of torsional vibrations in an elastic column are well known in the art, this system will not be described further.

After securing the frequency-measuring system in place, a torsional force is applied to the upper portion of the drill string and thereafter released in order to cause free torsional oscillation of the pipe string. This may be accomplished by any suitable technique. For example, a sub having a lever arm welded thereto may be screwed into the upper joint of the kelly 6 and thereafter struck with a sledge hammer. Alternatively, such torsional oscillation may be caused by imparting a rapid twist to the kelly by means of a wrench which is attached to the kelly and thereafter struck with a sledge hammer. The torsional force may also be applied and released through use of the rotary table, as will be apparent to one skilled in the art.

Under the conditions just described, the drill string will behave as a quarter-wave or multiple quarter-wave torsional oscillator with a node occurring at a point within the subterranean location at which the pipe is stuck and an antinode occurring at the upper end of the drill string. The drill string will oscillate at a harmonic frequency according to the following equation:

wherein:

g is the gravitational constant, and p is the density of the material of which the pipe string is formed.

It will be recognized that A, f, g, and p may be expressed in any consistent units. Usually, A will be expressed in feet and f in cycles per second, with the remaining terms expressed in appropriate units as indicated.

Upon making the frequency measurements, the distance A may be determined in accordance with Equation 1. In most cases the pipe string will behave as quarterwave oscillator and n normally can be assumed to have a value of one. However, even in the absence of such an assumption, the value of A normally can be ascertained by Equation 1 in light of a knowledge of local drilling conditions by correlating the possible values of A with locations which are known to be susceptible to conditions such as wellbore caving.

After having determined the depth at which the pipe string is stuck, preferably by the above-described method but by other techniques if desired, the pipe string then may be loosened in accordance with the present invention. In this embodiment of the invention, the pipe string is secured against torsional vibration thereof at a first point. Torsional vibrations then are applied to the pipe string at a second point such that significant torsional displacement of the pipe string is forced to occur at a third point within the location at which the pipe is stuck.

This embodiment of the invention will be described with reference to FIGURE 2 in which like elements are indicated by the same reference characters as are used in FIGURE 1. In carrying out this embodiment of the invention, the pipe string is secured against torsional vibration at a first point, hereinafter referred to as P adjacent the surface of the well. This may be accomplished as shown in FIGURE 2 by fastening the pipe string 4 in a suitable clamp 40 which, in turn, is rigidly fastened to the derrick structure 14 through spider arms such as shown at 42, 44 and 46. Torsional vibration then is applied to the pipe string at a second point, hereinafter referred to as P by means of a torsional oscillator 50. The torsional oscillator 50 may be of any suitable type. For example, it may take the form of a torsional vibration generator such as that disclosed in US. Patent No. 3,152,642 to Bodine.

While it usually will be prefererd to clamp the drill string up in the derrick as shown and apply the torsional vibrations in the vicinity of the derrick floor, this scheme of operation may be reversed. For example, the drill string may be securely clamped in the rotary table, e.g., by means of shims interposed between the kelly and kelly bushing, and the rotary table then locked against rotational movement. For example, the rotary table may be bolted to the floor 24 or otherwise secured to the derrick substructure. The torsional vibrations then may be applied to the drill string at a suitable location above the derrick floor.

As noted previously, the pipe string is torsionally vibrated at a frequency such that quarter-wave or multiple quarter-wave oscillations occur between the point P at which the pipe string is secured against torsional vibration and the point P at which torsional vibrations are applied. Thus, torsional vibrations are applied to the pipe string at a frequency producing a wave length A which satisfies the following equation:

In addition, such torsional vibrations are applied under conditions resulting in amaximum or near-maximum displacement amplitude Within the stuck location. More particularly, torsional vibrations are applied to the pipe .8L, an -1 (4) wherein:

n is an integer of the arithmetic progession, n =2,

L is the distance between the above-described points,

P and P It is preferred in carrying out the invention to operate at a relatively low frequency in order to avoid excessive attenuation of the. torsional oscillations between the surface and thesubterranean location at which the pipe string is stuck. Therefore, the drill string preferably is vibrated at a frequency producing quarter-wave oscillations between points P and P or; in terms of Equation 2, the pipe string is vibrated at a frequency such that the value of n is one. To further enable operations to be carried out within relativelylow frequency ranges it also is preferred to clamp the pipe string at point P a significant distance from the point P at which forced torsional vibrations are applied. Thus, as shown in FIGURE 2, it usually will be desirable to add one or more pipe joints 51 to the kelly 6 and to clamp the pipe string near the upper end of the pipe as indicated. In so-called triple joint rigs, i.e., drilling rigs which will accommodate three joints of drill pipe above the rotary table, it usually will be possible to provide a spacing of at least 90 feet between points P and P and this is preferred in carrying out the invention. In the smaller, double joint rigs this distance usually will not be attainable but, in this case, it will be preferred to provide at least 60 feet between points P and P Smaller distances between these points may be provided in accordance with the invention. However, in most cases it usually will be desirable to provide at least 3 feet between points P and P in order to avoid unacceptably high attenuation of the torsional vibrations as they are transmitted between points P and P While the application of torsional vibrations in accordance with Equations 2, 3, and 4 will assure the occurrence of significant torsional displacement at the stuck location, it is preferred to carry out the invention under conditions such that the distance L between points P and P is a whole number of half-wave lengths and a torsional displacement antinode occurs at the point P Thus, in accordance with this preferred embodiment of the invention, the pipe string is torsionally vibrated at a frequency f as defined by the following equations:

fi my 1-21 P wherein: n is an integer of the arithmetic progression n =l,3,5..., n is an integer of the arithmetic progression n =1, 2, 3 ,and

,u, g, p, l, and L are as defined above.

Preferably, where space limitations permit, the points P and P are selected such that f is equal to a natural frequency of torsional oscillation of the drill string so that a torsional resonant standing wave is set up in the drill string with a node at P and antinodes at P and P Preferably 11 of Equation 5 is assigned a value of one in order to produce quarter-wave oscillation between points P and P Also, it is preferred in carrying out this embodiment of the invention to provide a distance 1 between points P and P in accordance with the above described criteria.

Having described specific embodiments of the instant invention, it will be understood that further modifications thereof may be suggested to those skilled in the art, and it is intended to cover all such modifications as fall within the scope of the appended claims.

What is claimed is:

1. In a method of loosening a pipe string stuck at a subterranean location within a well, the steps comprising:

(a) securing said pipe string against torsional vibration at a first point P and (b) applying to said pipe string at a second point P torsional vibrations at a frequency producing a wavelength A satisfying the relationship:

relationships:

8L AP 211., 1

wherein:

L is the distance between P and a point P at the subterranean location at which the pipe is stuck, and

n is an integer of the arithmetic progression 2. The method of claim 1 wherein n is one. 3. The method of claim 2 wherein the distance I is at least 3 feet.

4. The method of claim 2 wherein the distance I is at least 60 feet.

5. The method of claim 2 wherein the distance I is at least feet.

6. In a method of loosening a pipe string stuck at a subterranean location within a well, the steps comprising: (a) securing said pipe string against torsional vibration at a first point P and (b) applying to said pipe string at a second point P torsional vibrations at a frequency f satisfying the relationships:

wherein:

n is an integer of the arithmetic progression n =l,3,5 n is an integer of the arithmetic progression n =l,2,3 ,u. is the shear modulus of the material of which said pipe string is formed, g is the gravitational constant, p is the density of the material of which the pipe string is formed, 1 is the distance between P and P and L is the distance between P and a point P at the subterranean location at which the pipe is stuck. 7. The method of claim 6 wherein n is one. 8. The method of claim 6 wherein the distance I is at least 3 feet.

9. The method of claim 6 wherein the distance I is at least 60 feet.

10. The method of claim 6 wherein the distance 1 is at least 90 feet.

11. In a method of determining the subterranean location at which a pipe string is stuck within a wellbore, the steps comprising:

(a) maintaining the upper portion of said pipe string adjacent the surface of said well in a condition permitting rotational movement,

(b) applying a torsional force on the upper portion of said pipe string,

(c) releasing said torsional force to cause free torsional oscillation of said pipe string, and

(d) measuring the frequency of said torsional oscillation to determine the location at which said pipe string is stuck.

12. The method of claim 11 further comprising loosening said pipe string by the subsequent steps of:

(e) securing said pipe string against torsional vibration at a first point P adjacent the surface of the well, and

(f) applying torsional vibrations to said pipe string at a second point P adjacent the surface of the well at a frequency f satisfying the relationships:

:2 L y" f1 2L p wherein:

n is an integer of the arithmetic progression n is an integer of the arithmetic progression p. is the shear modulus of the material of which said pipe string is formed,

3 is the gravitational constant,

p is the density of the material of which the pipe string is formed,

l is the distance between P and P and L is the distance between P and a point P at the subterranean location at which the pipe is stuck.

13. The method of claim 12 wherein n;, is one.

14. The method of claim 12 wherein the distance I is at least 3 feet.

15. The method of claim 12 wherein said pipe string comprises a drill string utilized in the rotary drilling of said well, the step of prior to step (e) adding at least one joint of pipe to said drill string and providing one of said points P and P on said at least one joint of pipe a distance of at least feet from the other of said points P and P 16. The method of claim 15 wherein said drill string is secured at said point P on said at least one joint of pipe.

References Cited UNITED STATES PATENTS 2,975,846 3/1961 Bodine --55 X 3,152,642 10/1964 Bodine 16646 CHARLES E. OCONNELL, Primary Examiner.

I. A. CALVERT, Assistant Examiner. 

1. IN A METHOD OF LOOSENING A PIPE STRING STUCK AT A SUBTERRANEAN LOCATION WITHIN A WELL, THE STEPS COMPRISING: (A) SECURING SAID PIPE STRING AGAINST TORSIONAL VIBRATION AT A FIRST POINT P1, AND (B) APPLYING TO SAID PIPE STRING AT A SECOND POINT P2 TORSIONAL VIBRATIONS AT A FREQUENCY PRODUCING A WAVELENGTH $ SATISFYING THE RELATIONSHIP:
 11. IN A METHOD OF DETERMINING THE SUBTERRANEAN LOCATION AT WHICH A PIPE STRING IS STUCK WITHIN A WELLBORE, THE STEPS COMPRISING: (A) MAINTAINING THE UPPER PORTION OF SAID PIPE STRING ADJACENT THE SURFACE OF SAID WELL IN A CONDITION PERMITTING ROTATIONAL MOVEMENT, (B) APPLYING A TORSIONAL FORCE ON THE UPPER PORTION OF SAID PIPE STRING, (C) RELEASING SAID TORSIONAL FORCE TO CAUSE FREE TORSIONAL OSCILLATION OF SAID PIPE STRING, AND (D) MEASURING THE FREQUENCY OF SAID TORSIONAL OSCILLATION TO DETERMINE THE LOCATION AT WHICH SAID PIPE STRING IS STUCK. 